1. Field of the Invention
The present invention relates to an information processing apparatus having a function for executing a plurality of tasks in parallel, a multitask control method and a program recording medium stored with programs for making a computer to execute a plurality of tasks in parallel.
2. Description of the Related Art
In recent years, information processing apparatus capable of executing a plurality of tasks in parallel have been used in various fields. In such information processing apparatus (also called "multitask system"), there are cases that limitation may be imposed to the kinds of tasks which are executable in parallel depending on the hardware installed. However, it is configured, in principle, that a task may be added to a group of tasks to be executed in parallel every time a task is instructed by a user.
As described above, the conventional information processing apparatus are configured to instantly start a task which is instructed by a user to be executed. Accordingly, for example, when instructions are rendered to simultaneously execute a task to reproduce a video data file which includes motion-picture data and voice data, and is generally represented by an extension of file such as "AVI" or "MOV" representing data categories, and a task to reproduce a voice data file represented by an extension "WAV," as a result of the tasks being executed in parallel as schematically shown in FIG. 12, disadvantages such as followings arise:
(1) When the reproduction of a first video data (extension "AVI") and the reproduction of a second video data (extension "AVI") are instructed to be executed in parallel, a load on a processing circuit such as a CPU for processing video data is increased, and a processing speed thereof is lowered, so that the motion of the picture becomes not smooth. As a result, a user suffers a problem that it is difficult to see what kind of the motion picture is reproduced.
(2) When the reproduction of a first video data (extension "WAV") and the reproduction of a second video data (extension "WAV") are instructed to be executed in parallel, one voice data is interrupted to be reproduced in the middle of the reproduction, and then another voice data starts to be reproduced when a reproduction circuit (a sound circuit) cannot reproduce more than one voice data at a time. That is, the obtained result of the execution is against a user's intention to reproduce and listen to the voice data, respectively. Also, in case that the reproduction circuit can simultaneously reproduce a plurality of voice data, since the voice data are mixedly reproduced, the user is difficult to recognize what kind of voice data is reproduced.
(3) When the reproduction of a video data (extension "AVI") and the reproduction of a voice data (extension "WAV") are instructed to be executed in parallel, the reproductions of the voice data included in the video data and the voice data are effected under the condition of the above item (2). As a result, either situation is arisen where an execution result which is against the user's intention is obtained or it is difficult to recognize what kind of voices are reproduced.
As described above, executions of tasks in parallel to reproduce the motion-picture data (or a video data) and the voice data which are time sequence data cause a large load on the CPU and also affect the processing by other applications. Furthermore, since the execution result interferes with the user's sense, it causes the user's to be difficult to recognize the reproduced contents.
In the conventional information processing apparatus, in order to prevent such phenomena from occurring, as schematically shown in FIG. 13, it is required for the user to perform a job such as to instruct execution of a next task again after completion of each task (or after interrupting each task by operating an input apparatus such as a mouse and a keyboard).